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First exams 2025

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Non-Contact Forces (SL IB Physics)

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Ashika

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Non-Contact Forces

Non-Contact Forces

  • A non-contact force is defined as:

A force which acts at a distance, without any physical contact between bodies, due to the action of a field

  • Examples of non-contact forces include:
    • Gravitational force
    • Electrostatic force
    • Magnetic force

Gravitational force, Fg

  • The attractive force experienced by two objects with mass in a gravitational field e.g the force between a planet and a comet
    • Weight, on Earth, is the gravitational force of the Earth acting on an object with mass
      • F subscript g space equals space m g
  • Electrostatic force, Fe
    • A force experienced by charged objects in an electric field which can be attractive or repulsive e.g. the attraction between a proton and an electron

  • Magnetic force, Fm
    • A force experienced between magnetic poles in a magnetic field that can be attractive or repulsive e.g. the attraction between the north and south poles of magnets

forces-at-distance-igcse-and-gcse-physics-revision-notes

Examples of non-contact forces

Worked example

A child drags a sledge behind them as they climb up a hill.

Describe the contact and non-contact forces acting on the child and the sledge.

Answer:

Step 1: Identify the contact forces acting on the child and the sledge

  • The child pulls on one end of the rope and the sledge pulls on the other end of the rope
    • This force is tension
  • The ground pushes against the child and the sledge
    • This is the normal contact force
  • The surface of the sledge moves over the the surface of the ground opposing the motion of the sledge
    • This force is surface friction
  • The surfaces of the child's shoes move over the surface of the ground (enabling the child to walk)
    • This force is also surface friction
  • The child and the sledge move through the air 
    • This force is fluid resistance or drag

Step 2: Identify the non-contact forces acting on the child and the sledge

  • The gravitational pull of the Earth acts on the child and the sledge
    • This force is weight

Examiner Tip

You will often see weight as W rather than Fg, even on the IB exam papers. It is always best to stick with whichever symbols you have been given in the question. However, if no symbols are given in the question, use the correct symbols from the syllabus (Fg).

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    Ashika

    Author: Ashika

    Expertise: Physics Project Lead

    Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.